GE EPM 6000 User manual

EPM 6000 Multi-function Power

Metering System

Chapter 1:

GE Consumer & Industrial

Multilin

EPM 6000

Instruction Manual

Software Revision: 4.5

Manual P/N: 1601-0215-A4

Manual Order Code: GEK-106558C

GE Multilin

215 Anderson Avenue, Markham, Ontario

Canada L6E 1B3

Tel: (905) 294-6222 Fax: (905) 201-2098

Internet:

http://www.GEmultilin.com

*1601-0215-A4*

ISO9001:2000

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GE Multilin's Quality

Management System is

registered to ISO9001:2000

QMI # 005094

LISTED

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE TOC–1

Table of Contents

1: OVERVIEW INTRODUCTION ................................................................................................................................ 1-1

D

ESCRIPTION ........................................................................................................................ 1-1

H

IGHLIGHTS ......................................................................................................................... 1-1

FEATURES ............................................................................................................................................ 1-3

U

NIVERSAL VOLTAGE INPUTS ............................................................................................ 1-3

C

URRENT INPUTS ................................................................................................................. 1-3

U

TILITY PEAK DEMAND ....................................................................................................... 1-3

M

EASURED VALUES ............................................................................................................ 1-4

ORDERING ........................................................................................................................................... 1-5

O

RDER CODES ..................................................................................................................... 1-5

SPECIFICATIONS ............................................................................................................................... 1-6

I

NPUTS/OUTPUTS ................................................................................................................ 1-6

M

ETERING ............................................................................................................................. 1-6

E

NVIRONMENTAL ................................................................................................................. 1-7

C

OMMUNICATIONS .............................................................................................................. 1-7

M

ECHANICAL PARAMETERS ................................................................................................ 1-7

A

PPROVALS ........................................................................................................................... 1-8

2: ELECTRICAL

BACKGROUND

THREE-PHASE POWER MEASUREMENT ................................................................................. 2-1

D

ESCRIPTION ........................................................................................................................ 2-1

THREE-PHASE SYSTEM CONFIGURATIONS ........................................................................... 2-2

D

ESCRIPTION ........................................................................................................................ 2-2

W

YE CONNECTION .............................................................................................................. 2-2

D

ELTA CONNECTION ........................................................................................................... 2-4

B

LONDELL'S THEOREM AND THREE-PHASE MEASUREMENT ........................................ 2-5

POWER, ENERGY, AND DEMAND .............................................................................................. 2-8

D

ESCRIPTION ........................................................................................................................ 2-8

P

OWER .................................................................................................................................. 2-8

E

NERGY ................................................................................................................................. 2-8

D

EMAND ...............................................................................................................................2-10

REACTIVE ENERGY AND POWER FACTOR ............................................................................. 2-12

R

EAL, REACTIVE, AND APPARENT POWER ........................................................................ 2-12

P

OWER FACTOR ................................................................................................................... 2-13

HARMONIC DISTORTION .............................................................................................................. 2-14

H

ARMONICS OF A NON-SINUSOIDAL WAVEFORM ......................................................... 2-14

I

NDUCTIVE AND CAPACITIVE IMPEDANCE ......................................................................... 2-15

V

OLTAGE AND CURRENT MONITORING ............................................................................ 2-15

W

AVEFORM CAPTURE ......................................................................................................... 2-16

POWER QUALITY .............................................................................................................................. 2-17

D

ESCRIPTION ........................................................................................................................ 2-17

3: INSTALLATION MECHANICAL INSTALLATION ..................................................................................................... 3-1

D

IMENSIONS ......................................................................................................................... 3-1

ANSI I

NSTALLATION STEPS ............................................................................................... 3-2

DIN I

NSTALLATION STEPS .................................................................................................. 3-3

ELECTRICAL INSTALLATION ......................................................................................................... 3-5

TOC–2 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

INSTALLATION CONSIDERATIONS .......................................................................................3-5

CT L

EADS TERMINATED TO METER ................................................................................... 3-6

CT L

EADS PASS-THROUGH (NO METER TERMINATION) ................................................ 3-6

Q

UICK CONNECT CRIMP CT TERMINATIONS ................................................................... 3-7

V

OLTAGE AND POWER SUPPLY CONNECTIONS .............................................................. 3-7

G

ROUND CONNECTIONS .................................................................................................... 3-8

WIRING DIAGRAMS ......................................................................................................................... 3-9

D

ESCRIPTION ........................................................................................................................ 3-9

W

YE, 4-WIRE WITH NO PTS AND 3 CTS, 3 ELEMENT ..................................................3-10

W

YE, 4-WIRE WITH NO PTS AND 3 CTS, 2.5 ELEMENT .............................................. 3-11

W

YE, 4-WIRE WITH 3 PTS AND 3 CTS, 3 ELEMENT .................................................... 3-12

W

YE, 4-WIRE WITH 2 PTS AND 3 CTS, 2.5 ELEMENT ................................................. 3-13

D

ELTA, 3-WIRE WITH NO PTS AND 2 CTS ..................................................................... 3-14

D

ELTA, 3-WIRE WITH 2 PTS AND 2 CTS ........................................................................ 3-15

C

URRENT-ONLY MEASUREMENT (THREE-PHASE) ..........................................................3-16

C

URRENT-ONLY MEASUREMENT (DUAL-PHASE) ............................................................ 3-17

C

URRENT-ONLY MEASUREMENT (SINGLE-PHASE) ......................................................... 3-18

COMMUNICATIONS SETUP .......................................................................................................... 3-19

D

ESCRIPTION ........................................................................................................................ 3-19

I

RDA COM1 PORT ............................................................................................................. 3-19

RS485 COM2 P

ORT ......................................................................................................... 3-19

4: USING THE METER FRONT PANEL INTERFACE ............................................................................................................ 4-1

D

ESCRIPTION ........................................................................................................................ 4-1

F

ACEPLATE ELEMENTS ........................................................................................................ 4-1

F

ACEPLATE BUTTONS .......................................................................................................... 4-2

P

ERCENTAGE OF LOAD BAR ...............................................................................................4-3

W

ATT-HOUR ACCURACY TESTING (VERIFICATION) ........................................................ 4-4

CONFIGURING THE METER VIA THE FRONT PANEL .......................................................... 4-5

O

VERVIEW ............................................................................................................................ 4-5

S

TART UP .............................................................................................................................. 4-5

M

AIN MENU ......................................................................................................................... 4-6

R

ESET MODE AND PASSWORD ENTRY .............................................................................4-6

CHANGING SETTINGS IN CONFIGURATION MODE ........................................................... 4-9

D

ESCRIPTION ........................................................................................................................ 4-9

C

ONFIGURING THE SCROLL FEATURE ............................................................................... 4-9

P

ROGRAMMING THE CONFIGURATION MODE SCREENS ................................................ 4-10

C

ONFIGURING THE CT SETTING ........................................................................................ 4-11

C

ONFIGURING THE PT SETTING ........................................................................................4-12

C

ONFIGURING THE CONNECTION SETTING ...................................................................... 4-13

C

ONFIGURING THE COMMUNICATION PORT SETTING .................................................... 4-14

OPERATING MODE ........................................................................................................................... 4-17

D

ESCRIPTION ........................................................................................................................ 4-17

5: COMMUNICATIONS MODBUS COMMUNICATIONS ..................................................................................................... 5-1

M

EMORY MAP DESCRIPTION ............................................................................................. 5-1

M

EMORY MAP ......................................................................................................................5-1

M

ODBUS MEMORY MAP NOTES ....................................................................................... 5-7

M

ODBUS MEMORY MAP DATA FORMATS ........................................................................ 5-9

DNP POINT MAPPING ..................................................................................................................... 5-10

DNP P

OINT MAPS ..............................................................................................................5-10

DNP P

OINT MAP NOTES ................................................................................................... 5-12

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE TOC–3

DNP IMPLEMENTATION ................................................................................................................. 5-13

O

VERVIEW ............................................................................................................................ 5-13

D

ATA LINK LAYER ................................................................................................................ 5-13

T

RANSPORT LAYER .............................................................................................................. 5-13

A

PPLICATION LAYER ............................................................................................................ 5-14

DNP OBJECTS AND VARIATIONS ............................................................................................... 5-15

D

ESCRIPTION ........................................................................................................................ 5-15

B

INARY OUTPUT STATUS (OBJECT 10, VARIATION 2) ................................................... 5-15

C

ONTROL RELAY OUTPUT (OBJECT 12, VARIATION 1) .................................................. 5-15

32-B

IT BINARY COUNTER WITHOUT FLAG (OBJECT 20, VARIATION 4) .................... 5-16

16-B

IT ANALOG INPUT WITHOUT FLAG (OBJECT 30, VARIATION 5) ......................... 5-16

C

LASS 0 DATA (OBJECT 60, VARIATION 1) ..................................................................... 5-17

I

NTERNAL INDICATIONS (OBJECT 80, VARIATION 1) ...................................................... 5-17

6: MISCELLANEOUS NAVIGATION MAPS ......................................................................................................................... 6-1

I

NTRODUCTION ..................................................................................................................... 6-1

M

AIN MENU SCREENS ........................................................................................................ 6-2

O

PERATING MODE SCREENS ............................................................................................. 6-3

R

ESET MODE SCREENS ....................................................................................................... 6-4

C

ONFIGURATION MODE SCREENS .................................................................................... 6-5

REVISION HISTORY .......................................................................................................................... 6-6

R

ELEASE DATES ................................................................................................................... 6-6

C

HANGES TO THE MANUAL ............................................................................................... 6-6

WARRANTY ......................................................................................................................................... 6-8

GE M

ULTILIN WARRANTY .................................................................................................. 6-8

TOC–4 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–1

EPM 6000 Multi-function Power

Metering System

Chapter 1: Overview

GE Consumer & Industrial

Multilin

Over view

1.1 Introduction

1.1.1 Description

The EPM 6000 is a multifunction power meter designed to be used in electrical substations,

panel boards and as a power meter for OEM equipment. The unit provides multifunction

measurement of electrical parameters.

The unit is designed with advanced measurement capabilities, allowing it to achieve high

performance accuracy. The EPM 6000 is specified as a 0.2% class energy meter for billing

applications as well as a highly accurate panel indication meter.

The EPM 6000 provides a host of additional capabilities, including standard RS485 Modbus

Protocol and an IrDA port remote interrogation.

1.1.2 Highlights

The following EPM 6000 features are detailed in this manual:

• 0.2% class revenue certifiable energy and demand metering

• Meets ANSI C12.20 (0.2%) and IEC 687 (0.2%) classes

• Multifunction measurement including voltage, current, power, frequency, energy

• Percentage of load bar for analog meter perception

• Easy-to-use faceplate programming

• IrDA port for PDA remote read

• RS485 Modbus communications

1–2 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 1: OVERVIEW

FIGURE 1–1: EPM 6000 Highlights

CHAPTER 1: OVERVIEW

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–3

1.2 Features

1.2.1 Universal Voltage Inputs

Voltage Inputs allow measurement to 416 V line-to-neutral and 721 V line-to-line. This

insures proper meter safety when wiring directly to high voltage systems. One unit will

perform to specification on 69 V, 120 V, 230 V, 277 V, and 347 V systems.

1.2.2 Current Inputs

The EPM 6000 current inputs use a unique dual input method.

• Method 1 – CT Pass Through: The CT passes directly through the meter without

any physical termination on the meter. This insures that the meter cannot be a

point of failure on the CT circuit. This is preferable for utility users when sharing

relay class CTs. No burden is added to the secondary CT circuit.

• Method 2 – Current “Gills”: This unit additionally provides ultra-rugged

termination pass-through bars that allow CT leads to be terminated on the meter.

This, too, eliminates any possible point of failure at the meter. This is a preferred

technique for insuring that relay class CT integrity is not compromised (the CT will

not open in a fault condition).

FIGURE 1–2: Current Input Connections

1.2.3 Utility Peak Demand

The EPM 6000 provides user-configured Block (fixed) or Rolling window demand. This

feature allows you to set up a customized demand profile. Block window demand is

demand used over a user-defined demand period (usually 5, 15, or 30 minutes). Rolling

window demand is a fixed window demand that moves for a user-specified subinterval

period. For example, a 15-minute demand using 3 subintervals and providing a new

demand reading every 5 minutes, based on the last 15 minutes.

1–4 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 1: OVERVIEW

Utility demand features can be used to calculate kW, kvar, kVA and PF readings. All other

parameters offer maximum and minimum capability over the user-selectable averaging

period. Voltage provides an instantaneous maximum and minimum reading which

displays the highest surge and lowest sag seen by the meter.

1.2.4 Measured Values

The EPM 6000 provides the following measured values all in real time and some

additionally as average, maximum, and minimum values.

Table 1–1: EPM 6000 Measured Values

Measured Values Real Time Average Maximum Minimum

Voltage L-N XXX

Voltage L-L XXX

Current per phase XXXX

Watts XXXX

vars XXXX

VA XXXX

Power Factor (PF) XXXX

Positive watt-hours X

Negative watt-hours X

Net watt-hours X

Positive var-hours X

Negative var-hours X

Net var-hours X

VA-hours X

Frequency XXX

%THD XXX

Voltage angles X

Current angles X

% of load bar X

CHAPTER 1: OVERVIEW

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–5

1.3 Ordering

1.3.1 Order Codes

The order codes for the EPM 6000 are indicated below.

For example, to order an EPM 6000 for 60 Hz system with a 1 A secondary CT input and no

THD or pulse output option, select order code PL6000-6-1A-0. The standard unit includes

display, all current/voltage/power/frequency/energy counters, percent load bar, RS485,

and IrDA communication ports.

Table 1–2: EPM 6000 Order Codes

PL6000 – * – * – *

Base Unit

PL6000 || |

EPM 6000 Power Metering System

System

Frequency

5 | |

50 Hz AC frequency system

6 | |

60 Hz AC frequency system

Current Input

1A |

1 A secondary CT

5A |

5 A secondary CT

THD and Pulse Output

0

No THD or pulse output option

THD

THD, limit alarms, and 1 KYZ pulse output

1–6 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 1: OVERVIEW

1.4 Specifications

1.4.1 Inputs/Outputs

POWER SUPPLY

Range:..................................................................D2 Option: Universal, 90 to 265 V AC at 50/60Hz, or 100 to

370 V DC

D Option: 18 to 60 V DC

Power consumption:.....................................5 VA, 3.5 W

VOLTAGE INPUTS (MEASUREMENT CATEGORY III)

Range:..................................................................Universal, Auto-ranging up to 416 V AC L-N, 721 V AC L-L

Supported hookups:......................................3-element Wye, 2.5-element Wye, 2-element Delta,

4-wire Delta

Input impedance:...........................................1 MOhm/phase

Burden:................................................................0.0144 VA/phase at 120 Volts

Pickup voltage: ................................................10 V AC

Connection:.......................................................Screw terminal (see Voltage Connection on page 3–8)

Maximum input wire gauge: ....................AWG #12 / 2.5 mm

2

Fault withstand: ..............................................Meets IEEE C37.90.1

Reading:..............................................................Programmable full-scale to any PT ratio

CURRENT INPUTS

Class 10:..............................................................5 A nominal, 10 A maximum

Class 2: ................................................................1 A nominal, 2 A maximum

Burden:................................................................0.005 VA per phase maximum at 11 A

Pickup current:.................................................0.1% of nominal

Connections:.....................................................O or U lug (see CT Leads Terminated to Meter on page 3–

6);

Pass-through wire, 0.177" / 4.5 mm maximum diameter

(see Pass-Through Wire Electrical Connection on page

3–7);

Quick connect, 0.25" male tab

(see Quick Connect Electrical Connection on page 3–7)

Fault Withstand:..............................................100 A / 10 seconds, 300 A / 3 seconds, 500 A / 1 second

Reading:..............................................................Programmable full-scale to any CT ratio

1.4.2 Metering

MEASUREMENT METHODS

Voltage and current:.....................................true RMS

Power:..................................................................sampling at 400+ samples/cycle on all channels

measured; readings simultaneously

A/D conversion:...............................................6 simultaneous 24-bit analog-to-digital converters

UPDATE RATE

Watts, vars, and VA: ......................................100 ms (10 times per second)

All other parameters:....................................1 second

CHAPTER 1: OVERVIEW

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 1–7

ACCURACY

NOTE: Typical results are more accurate.

1.4.3 Environmental

TEMPERATURE AND HUMIDITY

Storage:...............................................................–40 to 85°C

Operating:..........................................................–30 to 70°C

Humidity:............................................................up to 95% RH, non-condensing

Faceplate rating: ............................................NEMA 12 (water resistant), mounting gasket included

1.4.4 Communications

COMMUNICATIONS FORMAT

Types:...................................................................RS485 port through back plate

IrDA port through face plate

COMMUNICATIONS PORTS

Protocol:..............................................................Modbus RTU, Modbus ASCII, DNP 3.0

Baud rate: ..........................................................9600 to 57600 bps

Port address: ....................................................001 to 247

Data format:.....................................................8 bits, no parity

1.4.5 Mechanical Parameters

DIMENSIONS

Size:.......................................................................4.25" × 4.82" × 4.85" (L × W × H)

105.4 mm × 123.2 mm × 123.2 mm (L × W × H)

Mounting:...........................................................mounts in 92 mm square DIN or ANSI C39.1 4-inch round

cut-out

Weight:................................................................2 pounds / 0.907 kg

Shipping..............................................................ships in 6-inch / 152.4 mm cube container

Measured Parameters Display Range Accuracy

Voltage L-N 0 to 9999 kV or scalable 0.1% of reading

Voltage L-L 0 to 9999 V or kV scalable 0.1% of reading

Current 0 to 9999 A or kA 0.1% of reading

+/– Watts 0 to 9999 W, kW, or MW 0.2% of reading

+/– Wh 5 to 8 digits (programmable) 0.2% of reading

+/– vars 0 to 9999 vars, kvars, Mvars 0.2% of reading

+/– varh 5 to 8 digits (programmable) 0.2% of reading

VA 0 to 9999 VA, kVA, MVA 0.2% of reading

VAh 5 to 8 digits (programmable) 0.2% of reading

Power Factor (PF) ±0.5 to 1.0 0.2% of reading

Frequency 45 to 65 Hz 0.01 Hz

% THD 0 to 100% 2.0% F.S.

% Load Bar 10 digit resolution scalable 1 to 120% of reading

1–8 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 1: OVERVIEW

1.4.6 Approvals

TYPE TESTING

IEC 687 (0.2% accuracy)

ANSI C12.20 (0.2% accuracy)

ANSI (IEEE) C37.90.1: ....................................Surge Withstand

ANSI C62.41 (burst)

IEC 1999-4-2: ...................................................ESD

IEC 1000-4-3: ...................................................Radiated Immunity

IEC 1000-4-4: ...................................................Fast Transient

IEC 1000-4-5: ...................................................Surge Immunity

COMPLIANCE

ISO: ........................................................................manufactured to an ISO9001 registered program

UL:..........................................................................UL listed (file E250818)

CSA:.......................................................................Certified per: C22.2 No.1010.1 Electrical and Electronic

Measuring and Testing Equipment

CE:..........................................................................conforms to EN 55011 / EN 50082

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–1

EPM 6000 Multi-function Power

Metering System

Chapter 2: Electrical Background

GE Consumer & Industrial

Multilin

Electric al Background

2.1 Three-Phase Power Measurement

2.1.1 Description

This introduction to three-phase power and power measurement is intended to provide

only a brief overview of the subject. The professional meter engineer or meter technician

should refer to more advanced documents such as the EEI Handbook for Electricity

Metering and the application standards for more in-depth and technical coverage of the

subject.

2–2 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 2: ELECTRICAL BACKGROUND

2.2 Three-Phase System Configurations

2.2.1 Description

Three-phase power is most commonly used in situations where large amounts of power

will be used because it is a more effective way to transmit the power and because it

provides a smoother delivery of power to the end load. There are two commonly used

connections for three-phase power, a wye connection or a delta connection. Each

connection has several different manifestations in actual use. When attempting to

determine the type of connection in use, it is a good practice to follow the circuit back to

the transformer that is serving the circuit. It is often not possible to conclusively determine

the correct circuit connection simply by counting the wires in the service or checking

voltages. Checking the transformer connection will provide conclusive evidence of the

circuit connection and the relationships between the phase voltages and ground.

2.2.2 Wye Connection

The wye connection is so called because when you look at the phase relationships and the

winding relationships between the phases it looks like a wye (Y). The following figure

depicts the winding relationships for a wye-connected service. In a wye service the neutral

(or center point of the wye) is typically grounded. This leads to common voltages of 208/

120 and 480/277 (where the first number represents the phase-to-phase voltage and the

second number represents the phase-to-ground voltage).

FIGURE 2–1: Three-Phase Wye Winding

The three voltages are electrically separated by 120°. Under balanced load conditions with

unity power factor, the currents are also separated by 120°. However, unbalanced loads

and other conditions can cause the currents to depart from the ideal 120° separation.

Three-phase voltages and currents are usually represented with a phasor diagram. A

phasor diagram for the typical connected voltages and currents is shown below.

Ia

Vbn

A

B

C

Van

Vcn

N

CHAPTER 2: ELECTRICAL BACKGROUND

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–3

FIGURE 2–2: Three-Phase Voltage and Current Phasors for Wye Winding

The phasor diagram shows the 120° angular separation between the phase voltages. The

phase-to-phase voltage in a balanced three-phase wye system is 1.732 times the phase-

to-neutral voltage. The center point of the wye is tied together and is typically grounded.

The following table indicates the common voltages used in the United States for wye-

connected systems.

Usually, a wye-connected service will have four wires: three wires for the phases and one

for the neutral. The three-phase wires connect to the three phases. The neutral wire is

typically tied to the ground or center point of the wye (refer to the Three-Phase Wye

Winding diagram above).

In many industrial applications the facility will be fed with a four-wire wye service but only

three wires will be run to individual loads. The load is then often referred to as a delta-

connected load but the service to the facility is still a wye service; it contains four wires if

you trace the circuit back to its source (usually a transformer). In this type of connection

the phase to ground voltage will be the phase-to-ground voltage indicated in the table

above, even though a neutral or ground wire is not physically present at the load. The

transformer is the best place to determine the circuit connection type because this is a

location where the voltage reference to ground can be conclusively identified.

Table 2–1: Common Phase Voltages on Wye Services

Phase-to-Ground Voltage Phase-to-Phase Voltage

120 volts 208 volts

277 volts 480 volts

2400 volts 4160 volts

7200 volts 12470 volts

7620 volts 13200 volts

Van

Vcn

Vbn

Ic

Ib

Ia

2–4 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 2: ELECTRICAL BACKGROUND

2.2.3 Delta Connection

Delta connected services may be fed with either three wires or four wires. In a three-phase

delta service the load windings are connected from phase-to-phase rather than from

phase-to-ground. The following figure shows the physical load connections for a delta

service.

FIGURE 2–3: Three-Phase Delta Winding Relationship

In this example of a delta service, three wires will transmit the power to the load. In a true

delta service, the phase-to-ground voltage will usually not be balanced because the

ground is not at the center of the delta.

The following diagram shows the phasor relationships between voltage and current on a

three-phase delta circuit.

In many delta services, one corner of the delta is grounded. This means the phase to

ground voltage will be zero for one phase and will be full phase-to-phase voltage for the

other two phases. This is done for protective purposes.

FIGURE 2–4: Three-Phase Voltage and Current Phasors for Delta Winding

Ia

Ica

Iab

Ib

Ibc

Ic

Vab

Vbc

A

B

C

Vca

Vbc

Vca

Vab

Ic

Ib

Ia

CHAPTER 2: ELECTRICAL BACKGROUND

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 2–5

Another common delta connection is the four-wire, grounded delta used for lighting loads.

In this connection the center point of one winding is grounded. On a 120/240 volt, four-

wire, grounded delta service the phase-to-ground voltage would be 120 volts on two

phases and 208 volts on the third phase. The phasor diagram for the voltages in a three-

phase, four-wire delta system is shown below.

FIGURE 2–5: Three-Phase, Four-Wire Delta Phasors

2.2.4 Blondell's Theorem and Three-Phase Measurement

In 1893 an engineer and mathematician named Andre E. Blondell set forth the first

scientific basis for poly phase metering. His theorem states:

If energy is supplied to any system of conductors through N wires, the total power in the

system is given by the algebraic sum of the readings of N watt-meters so arranged that

each of the N wires contains one current coil, the corresponding potential coil being

connected between that wire and some common point. If this common point is on one

of the N wires, the measurement may be made by the use of N-1 wattmeters.

The theorem may be stated more simply, in modern language:

In a system of N conductors, N – 1 meter elements will measure the power or energy

taken provided that all the potential coils have a common tie to the conductor in which

there is no current coil.

Three-phase power measurement is accomplished by measuring the three individual

phases and adding them together to obtain the total three phase value. In older analog

meters, this measurement was made using up to three separate elements. Each element

combined the single-phase voltage and current to produce a torque on the meter disk. All

three elements were arranged around the disk so that the disk was subjected to the

combined torque of the three elements. As a result the disk would turn at a higher speed

and register power supplied by each of the three wires.

According to Blondell's Theorem, it was possible to reduce the number of elements under

certain conditions. For example, a three-phase, three-wire delta system could be correctly

measured with two elements (two potential coils and two current coils) if the potential coils

were connected between the three phases with one phase in common.

Vca

Vab

Vbc

Vnc

Vbn

120 V

2–6 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE

CHAPTER 2: ELECTRICAL BACKGROUND

In a three-phase, four-wire wye system it is necessary to use three elements. Three voltage

coils are connected between the three phases and the common neutral conductor. A

current coil is required in each of the three phases.

In modern digital meters, Blondell's Theorem is still applied to obtain proper metering. The

difference in modern meters is that the digital meter measures each phase voltage and

current and calculates the single-phase power for each phase. The meter then sums the

three phase powers to a single three-phase reading.

Some digital meters calculate the individual phase power values one phase at a time. This

means the meter samples the voltage and current on one phase and calculates a power

value. Then it samples the second phase and calculates the power for the second phase.

Finally, it samples the third phase and calculates that phase power. After sampling all three

phases, the meter combines the three readings to create the equivalent three-phase

power value. Using mathematical averaging techniques, this method can derive a quite

accurate measurement of three-phase power.

More advanced meters actually sample all three phases of voltage and current

simultaneously and calculate the individual phase and three-phase power values. The

advantage of simultaneous sampling is the reduction of error introduced due to the

difference in time when the samples were taken.

Blondell's Theorem is a derivation that results from Kirchhoff's Law. Kirchhoff's Law states

that the sum of the currents into a node is zero. Another way of stating the same thing is

that the current into a node (connection point) must equal the current out of the node. The

law can be applied to measuring three-phase loads. The figure below shows a typical

connection of a three-phase load applied to a three-phase, four-wire service. Kirchhoff's

Laws hold that the sum of currents A, B, C and N must equal zero or that the sum of

currents into Node “n” must equal zero.

FIGURE 2–6: Three-Phase Load Illustrating Kirchhoff’s Law and Blondell’s Theorem

Phase B

Phase C

Phase A

A

B

C

N

Node "n"

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GE EPM 6000, EPM 6000 Multi-function Power Metering System User manual

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